1. Field
The present invention relates to an arrangement for equalizing the rope force of an elevator. The invention also relates to an elevator.
2. Description of Related Art
It is becoming increasingly common to use large suspension ratios, e.g. 3:1 . . . 9:1 and even larger, in traction sheave elevators. This generally involves the problem that, due to the many rope loops used, hoisting ropes of great length are required. For the operation and safety of the elevator, it is essential that the hoisting rope portion of the hoisting ropes below the elevator car be kept sufficiently tightly tensioned, and thus the amount of rope elongation to be compensated, or equalized, is also large. Due to the length of the adjustment distance, it is difficult to implement the required rope compensation sufficiently effectively using prior-art rope compensation devices.
Another reason requiring long ropes may be a large hoisting height of the elevator. In this case, the length of the hoisting ropes used in the elevators is also large, and therefore elevators having a large hoisting height also require a compensation arrangement capable of compensating a large elongation. In such structures, large elongations produce problems already starting from 1:1 suspension.
The construction and quality of the materials used in elevator technology as well as the control and operating systems have improved so much that nowadays it is increasingly commonly possible to implement traction sheave elevators without using a counterweight at all. In these elevator solutions, proper and reliably functioning equalization of rope forces is very important.
The rope force equalizing solutions used in prior art include solutions in which the equalization is based on various spring and lever systems. These solutions use e.g. spring or lever systems with either end of the hoisting ropes secured to them. However, a problem with such solutions is the required length of adjustment distance, because the substantially short displacement of the spring or lever does not allow a large adjustment distance and consequently does not permit compensation of large elongations. This involves at least the problem that, in the case of large suspension ratios or when long hoisting ropes are otherwise used in tall buildings, equalization of rope forces is not possible because of the length of the adjustment distance.
A better solution for equalization in cases of a long distance to be compensated would be a compensating sheave, the rim of which allows a longer compensation distance for a hoisting rope fastened to the rim than the displacement of a spring or lever. As is known, such compensating sheaves have been used for this purpose, but they also involve certain problems. One of the problems is e.g. the fact that, due to its size, the fastening of the end of the hoisting rope on the compensating sheave takes up a large space. Therefore, a compensating sheave with the hoisting rope ends fastened to it in the traditional manner according to generally known technology would have to be of a very large size to allow the elements required for the fastening to be placed on the compensating sheave. This would lead to the problem of having a complicated, large and heavy compensating sheave that is difficult to dispose in a suitable place in conjunction with other structures of the elevator. Additionally, even when compensating sheaves are used, the adjustment distance is relatively short, and thus no very large elongations can be compensated.
International patent specification no. WO2004/067429 discloses several solutions for the compensation of rope elongations. Of these solutions, especially the described block and tackle arrangements work otherwise well except that they are primarily only suited to be placed in the shaft, separately from the car.